Ceramic seal runner and mount for a rotating shaft

ABSTRACT

A circumferential seal for a machine having a rotating shaft is provided. The seal may comprise a metallic mounting element and a ceramic sealing runner. The mounting element may be affixed around the shaft and comprise a base and a mounting member. The mounting member may extend radially outward from the base and axially along the shaft to form a radially inward facing cylindrical surface. The sealing runner may have a radially outward facing surface and be carried by said mounting element in axial and radial alignment by an interference fit between at least a portion of the radially outward facing surface of the runner and at least a portion of the radially inward facing surface of the mounting member.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/295,938, filed Feb. 16, 2016, the entirety of which is herebyincorporated by reference.

FIELD OF THE DISCLOSURE

The present disclosure is directed to systems and methods of formingseals in rotating machinery, and more particularly to a circumferentialseal for a machine having a rotating shaft.

BACKGROUND

In rotating machinery, the passages between fixed structures surroundingrotating components provide pathways for leakage of either the workingfluid or support system fluids. These pathways may allow fluid from thesupporting systems, such as lubricating oil, to leak into the workingfluid, or may allow the working fluid to leak into these supportsystems. These leaks along the shaft, or rotor, of the rotatingmachinery result in lower operating efficiency and quicker degradationof machine components requiring more frequency maintenance intervals.

To inhibit leakage through these pathways, rotating machines use variousseals and sealing techniques. Circumferential seals are commonly used toprevent fluid leakage between compartments. Controlled-gap seals,arch-bound circumferential seals, and segmented circumferentialcontacting seals are commonly used mechanical sealing methods forcircumferential seals. These seals comprise a rotating component, calleda seal rotor, sometimes known as a runner, and a non-rotating componentcalled a radial seal or a carbon circumferential seal.

A common configuration is a seal rotor composed of a metallic materialand a radial seal composed of carbon (which may also be referred to as acircumferential carbon seal or a carbon circumferential seal). Thisconfiguration exhibits a high degree of friction between the rotor andradial seal which wears the carbon seal quickly, resulting in the needfor more frequent inspection and replacement. To avoid this friction atthe sealing interface, the machine may be designed with a small gapbetween the metallic seal rotor and the carbon circumferential seal.However, the difference in the coefficients of thermal expansion (CTE),as well as the amount of mechanical growth due to centrifugal effects,between a metallic seal rotor and a carbon circumferential seal is suchthat it is difficult to maintain this small gap. The carboncircumferential seal and metallic seal rotor will expand at differentrates as the machine operating temperature changes and at differentmachine speeds. Consequently, the gap will either be too large forefficient operation, or will be too small resulting in excessive wear tothe circumferential carbon seal.

One solution to this high wear rate is to replace the metallic sealrotor with a ceramic runner. A ceramic runner may be chosen with a CTEclose to that of a carbon circumferential seal. Ceramic materials mayalso experience less mechanical growth from centrifugal effects due tohigh elastic modulus. The thermal expansion and elastic modulus ofceramic materials allow tighter gaps to be maintained over the operatingrange of the machine, thereby avoiding some of the above consequences ofusing a metallic rotor. Additionally, the ceramic material may have alower frictional force between itself and the circumferential carbonseal. The ceramic material may have a sufficiently low frictional forcewith the carbon seal that the two may be in contact during operationwithout significant wear to the seal.

However, the use of ceramic materials imposes challenges in theapplication of a high temperature machinery, such as a jet engine. Aceramic runner must circumscribe and be affixed, directly or indirectly,to the metallic shaft of the machine. Differences between the CTE of theceramic and metallic components result in varying stresses on theceramic component as a result of the differences in thermal growth astemperatures change during machine operations. Additionally, somerotating machines are assembled such that subcomponents are stacked uponone another around the shaft and held together by large compressiveforces, a method also known as a lockup assembly. These largecompressive forces can create tensile stresses in portions of a ceramicrunner. Ceramics may crack under these tensile stresses because they arebrittle in nature.

SUMMARY

The present application discloses one or more of the features recited inthe appended claims and/or the following features which, alone or in anycombination, may comprise patentable subject matter.

According to an aspect of the present disclosure, a circumferential sealfor a machine having a rotating shaft is provided. The seal may comprisea metallic mounting element affixed around the circumference of theshaft and a ceramic sealing runner. The mounting element may comprise abase forming a radially outward facing cylindrical surface extendingaxially along the shaft and a mounting member extending radially outwardfrom the base and axially along the shaft forming a radially inwardfacing cylindrical surface which extends axially along the shaft adistance less than the outward facing cylindrical surface of the base.The runner has a radially outward facing cylindrical surface extendingaxially along the shaft a distance greater than the radially outwardfacing cylindrical surface of the base, and the runner is carried by themounting element in axial and radial alignment by an interference fitbetween at least a portion of the radially outward facing cylindricalsurface of the runner and at least a portion of the radially inwardfacing cylindrical surface of the mounting member.

In some embodiments, the mounting member may be radially compliant. Insome embodiments the mounting member further forms an extensionprojecting radially outward from the base, an axial extending member andan axial return member which forms the radially inward facing surface ofthe mounting member. In some embodiments the extension, the axiallyextending member and the axial return member form a radially compliantopening in the mounting member. In some embodiments the axiallyextending member is arcuate.

In some embodiments the mounting member further comprises a fluidflinger disposed on a radial outer surface of the mounting member. Insome embodiments the sealing runner experiences its highest stress loadduring assembly, or when the engine is off and at lower ambienttemperatures. In some embodiments the stress load on the sealing runnerdecreases with increasing temperature.

In some embodiments the circumferential seal further comprises a radialseal for sealingly engaging the outer radially outward facing surface ofthe sealing runner. In some embodiments the radial seal comprisescarbon.

In some embodiments the interference fit is proximate an axial end ofthe sealing runner. In some embodiments the base further forms aradially inner surface at an angle to an axis of the machine. In someembodiments the radially outward facing surface of the base and therunner define an opening for operably engaging a flexible sealingelement. In some embodiments the flexible sealing element is an O-ring.

According to another aspect of the present disclosure, a circumferentialseal for a machine having a metallic rotating shaft comprises a mountingelement affixed around a circumference of the shaft, the mountingelement comprising: a base forming a radially outward facing surfaceextending axially along the shaft; and a mounting member, wherein themounting member forms an extension projecting radially outward from thebase, an axial extending member and an axial return member which forms aradially inward facing cylindrical surface. In some embodiments theextension, the axially extending member and the axial return member forma radially compliant opening in the mounting member. In some embodimentsa sealing runner having a radially outward facing cylindrical surfaceextending axially along the shaft, the sealing runner being carried bythe mounting element in axial and radial alignment by an interferencefit between at least a portion of the radially outward facingcylindrical surface of the ceramic sealing runner and at least a portionof the radially inward facing cylindrical surface of the mountingmember.

According to another aspect of the present disclosure, a method offorming a circumferential seal in a machine having a metallic rotatableshaft comprises affixing a metallic mounting element around thecircumference of the shaft, the mounting element comprising a baseforming a radially outward facing cylindrical surface extending axiallyalong the shaft, and a mounting member extending radially outward fromthe base and axially along the shaft forming a radially inward facingcylindrical surface extending axially along the shaft a distance lessthan the radially outward facing cylindrical surface of the base; andproviding a ceramic sealing runner having a radially outward facingcylindrical surface extending axially along the shaft a distance greaterthan the radially outward facing cylindrical surface of the base, theceramic sealing runner being carried by the mounting element in axialand radial alignment by an interference fit between at least a portionof the radially outward facing cylindrical surface of the ceramicsealing runner and at least a portion of the radially inward facingcylindrical surface of the mounting member.

In some embodiments the mounting member of the mounting element isradially compliant. In some embodiments the method further comprisessealingly engaging the outer radially outward facing surface of thesealing runner with a radial seal. In some embodiments the sealingrunner experiences its highest stress load during assembly, when theengine is off, or both. Also, the cooler the engine becomes while off,the greater the stress in the ceramic becomes.

These and many other advantages of the present subject matter will bereadily apparent to one skilled in the art to which the disclosurepertains from a perusal of the claims, the appended drawings, and thefollowing detailed description of preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional, axial view of a prior art circumferentialseal.

FIG. 2 is a cross-sectional, axial view of a second prior artcircumferential seal.

FIG. 3A is a cross sectional, axial view of a mounting element accordingto some embodiments of the present disclosure.

FIG. 3B is a perspective view of a mounting element cross-sectionaccording to some embodiments of the present disclosure.

FIG. 4 is a cross sectional, axial view of a mounting element accordingto some embodiments of the present disclosure.

While the present disclosure is susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and will be described in detail herein. Itshould be understood, however, that the present disclosure is notintended to be limited to the particular forms disclosed. Rather, thepresent disclosure is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the disclosure asdefined by the appended claims.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thedisclosure, reference will now be made to a number of illustrativeembodiments illustrated in the drawings and specific language will beused to describe the same.

FIG. 1 illustrates a cross-sectional, axial view of a prior artcircumferential seal 100. The seal 100 comprises ceramic runner 106which engages a carbon circumferential seal (not shown). The axial andradial alignment of ceramic runner 106 is maintained about shaft 104 byannular clamping members 108 and 110. These annular clamping members 108and 110 are disposed between parts 116 and 114. Part 116 may be abearing race or other clamped component, or part 116 may be a threadednut used to supply a clamping force used to secure annular clampingmembers 108 and 110 to the shaft 104. This clamping force may passthrough an optional spacer 114 to a shoulder 112 of the shaft 104. Shaft104 rotates about axis 102.

The ceramic runner 106 includes a radially inward extending flange froma main cylindrical body which engages the clamping members 108, 110.This flange is adapted to receive the clamping force transmitted betweenthe annular clamping members. Clamping member 110 has a length andthickness which allows for some radial flexibility. The annular member108 may include circumferentially extending slots (not shown) whichallow the annular member 108 to expand and contract, thereby impartingaxial flexibility.

FIG. 2 illustrates a cross-sectional, axial view of another prior artcircumferential seal 200. Seal 200 comprises a ceramic runner 206 whichengages a circumferential carbon seal (not shown). Runner 206 is fixedto shaft 204 via clamp members 208 and 210. Clamp member 210 has alength and thickness designed to impart radial flexibility. Clamp member208 retains the axial spring 218. The axial spring provides an axialclamping force on runner 206. Shaft 204 rotates about axis 202.

While the above circumferential seals provide a means for mounting aceramic runner to a shaft, the small CTE of a ceramic runner compared tothe metallic mounting components and metallic shaft, as well as the lowflexural strength of the ceramic runner still present problems duringthe operation of the machine. First, these ceramic seals require twocomponents to provide axial and radial alignment. Using two componentsincreases design, production, assembly and maintenance costs. Second,the use of slots on axial support members, or springs between an axialsupport member and the ceramic runner provide additional leakagepathways. Third, as the temperature of machine rises, the metallicsupport members will expand more than the ceramic runner due to thehigher CTE of the metal components. This greater expansion of the metalcomponents will increase the stress in the ceramic runner when it ismounted on its inner diameter. Fourth, the runner illustrated in theabove figures each require a radially inward extending flange to whichthe mounting components are engaged. This increases the complexity ofthe runner design, and may directly subject at least this runner flangeto the lock-up loading resulting from the machine assembly.

As disclosed in some embodiments herein, the current subject matteraddresses these deficiencies by utilizing a single metallic mountingmember which provides an interference fit with the outer diameter ofceramic runner. The current subject matter holds the axial and radialalignment of the ceramic runner with smaller radial deflection andconcentricity with the shaft centerline without overstressing theceramic runner.

In accordance with some embodiments of the present disclosure, acircumferential seal for a rotating machine is presented. With referenceto FIGS. 3A-3B, an axial view of a cross section of a circumferentialseal 300 is illustrated. The seal 300 comprises mounting element 320 andrunner 306, which may also be known as a sealing rotor. The mountingelement 320 is affixed around a circumference of shaft 304 having arotational axis 302, and comprises a base 322 and a mounting member 326.The mounting element 320 may comprise a metal or metal alloy. The seal300 may further comprise a carbon circumferential seal, or radial seal(not shown) sealingly engaging an outer surface of runner 306.

The base 322 forms the radially innermost portion of mounting element320, and may be in direct contact with shaft 304. The base 322 defines aradial outer surface 324 which extends axially along the shaft 304 andmay be referred to as a radially outward facing surface. The radialouter surface 324 may define a concentric cylinder, although it is notso limited. The radial outer surface 324 may also partially define anopening 342 in base 322 configured to receive a flexible sealingelement. Various sealing elements may be used to include O-rings, omegaseals, or other sealing methods known to one of skill in the art. Thesesealing elements may function as a secondary seal in case any fluidleaks between the mounting element 320 and the runner 306.

In accordance with some embodiments, the base 322 may further define aradially inward surface or flange 340 on an oil or non-working fluidside of the seal 300. Surface 340 may be at an angle relative to theaxis 302, such that surface 340 will direct any oil or other fluid intoa sump or other location (not shown). The oil or other fluid will bedirected along the surface by a centrifugal force due to the rotation ofshaft 304.

The base 322 provides a means for maintaining the mounting element 320in an axial position on said shaft 304. In some embodiments, themounting element is subjected to an axial compressive force resultingfrom the assembly of the machine. This force may be transferred from orto components 344 and 314. Due to the complexities of machine design,components 344 and 314 could be any of a number of parts of a rotatingmachine: a spacer designed to transfer load to another component, ashoulder machined onto the shaft 304, a bearing race used to support theshaft 304, or a nut used to generate the axial compressive force arejust a few of possible parts from which components 344 and 314 may beselected. A person of ordinary skill will recognize that thesecomponents are selected to meet the overall design requirements of themachine, and may include parts which are not listed above.

Extending in a radially outward direction from the base 322 is mountingmember 326. The mounting member 326 also extends axially to define aradially inward facing surface 328. In some embodiments, the inwardfacing surface 328 may extend axially along the shaft 304 for a distanceless than the outward facing surface 324 of the base 322. The inwardfacing surface 328 may be located between the axially extreme portionsof the outward facing surface 324, or may be axially displaced from theoutward facing surface 324. The inward facing surface 328 is used toprovide an interference fit with the runner 306. An interference fitoccurs when the inner diameter, measured from the axis 302, of the to-beoutboard component is slightly smaller than the outer diameter to theto-be inboard component. Additionally, a large residual assembly stressmay be placed on the components. This interference fit may occurproximate the axial ends of the runner 306, although it may occurelsewhere on the runner 306. In some embodiments, the inward facingsurface 328 is cylindrical.

The interference fit between the surface 328 and the runner 306 may beengineered such that it is sufficient to maintain the axial alignment ofthe runner 306 to the shaft 304. Additionally, the residual mountingstress imparted to the runner 306 from the mounting member 326 aroundthe circumference of the shaft 304 will maintain the runner 306 inradial alignment relative to the shaft 304.

In some embodiments, the mounting member 326 comprises radial extension334, axial extending member 332 and an axial return member 331 whichforms the radially inward facing surface 328. Radial extension 334extends radially from the base 322, connecting axial extending member332 to the base 322. Axial extending member 332 may extend axially andradially from radial extension 334 to join extension 334 and the axialreturn member 331. While axial extending member 332 is shown as having agenerally curved or arcuate body, it should be understood that member332 need not be curved, nor, if curved, be curved with a constantradius.

The axial return member 331, axial extending member 332 and extension334 may define an opening 336 in the mounting member 326. The size ofthe opening 336 may be designed by controlling the dimensions of theabove mentioned components in order to control the amount of stressimparted to the runner 306 at various operating conditions of themachine. Opening 336 allows the mounting member 326 to be radiallycompliant such that stresses imparted to runner 306 are maintainedwithin acceptable limits at all operating conditions.

Engaging the radially outward facing surface 330 of the runner 306 withthe mounting member 326 provides an apparatus designed to impart thehighest stress levels in the runner 306 at the lowest operatingtemperatures, which may occur during or shortly following assembly.Selection of the CTE of the runner 306 and mounting member 326 providesthe opportunity to select materials with a higher CTE for the mountingmember 326 than the runner 306. As the temperature of the machine rises,the expansion of the mounting member 326 may be greater than that of therunner 306, which will reduce the residual, interference fit stressesremaining in the runner 306 from initial loading. This is beneficialbecause the runner 306 can be checked for failure at its most stressedcondition: when the machine is cold and during assembly.

The runner 306 of seal 300 may comprise ceramic. The CTE of a ceramicmaterial is significantly lower than the CTE of metal and metal alloys.The above mentioned difficulties in maintaining ceramic materials withintolerable stress levels are significantly reduced when the axial andradial alignment are provided by the mounting element 320 engaging therunner 306 at its outer diameter. This puts the highest stress levels inthe ceramic in compression rather than tension. And since ceramics aremuch stronger in compression compared to tension, these highestcompression stresses are well below the allowed ceramic compressiveflexural strength.

In some embodiments, the runner 306 comprises a radially outward facingcylindrical surface 330 extending axially along the shaft 304. A personof ordinary skill will recognize that the runner 306 is not limited tothis particular shape over its entire or even a portion of its axiallength. The outward facing surface 330 may extend an axial distancegreater than mounting element 320, base 322, or both. The outward facingsurface 330 engages the inward facing surface 328 of mounting member 326via an interference fit, which maintains the axial and radial alignmentof runner 306. At least a portion of the radially outward facing surface330 and at least a portion of the radially inward facing surface 328 mayform the interference fit. The runner 306 may further comprise an innerradial or other retaining elements which may aid in the axial alignmentof runner 306. This retaining element may be a flange which engagesportions of the runner 306 or other components, e.g. component 344.

In accordance with some embodiments of the present disclosure, acircumferential seal for a rotating machine is presented. With referenceto FIG. 4, an axial view of a cross section of a circumferential seal400 is illustrated. Shaft 404, mounting element 420, base 422, outwardfacing surface 424, mounting member 426, inward facing surface 428,outward facing surface 430, components 414 and 444, surface 440 andrunner 406 may be as described above with reference to FIG. 3. In someembodiments, mounting member 426 may comprise fluid flinger 438 whichmay be radially extend from the mounting member 426. The fluid flinger438 functions to reduce the amount of fluid, e.g. oil, which may leakonto a circumferential carbon seal (not shown). Additionally, flinger438 may function to provide a more ready support for removing themounting element 420 from the machine. The flinger 438 is also used toprovide a more evenly distributed contact interface between the mountingfeature and the ceramic runner.

In some embodiments, the mounting member 426 may not include an openingto aid in radial compliance. Rather the mounting member 426 utilizes theextra material, when compared to embodiments with an opening, to stiffenthe inward facing surface 428. The flinger 438 may comprise this extramaterial. This stiffness gives better surface contact between thesurface 428 and runner 406, and leads to a more robust design.

The present disclosure provides for mounting a runner by engaging itsradially outer facing surface using an interference fit. This providesthe benefits of subjecting the runner to the highest stress levelsduring assembly and at temperatures lower than operating temperatures,when the runner can be checked at its highest stressed condition. Therunner will be subjected to a decreasing stress as the mounting elementexpands more than the runner. Another benefit is that the runner will besubject to higher compression forces than tensions forces. This isimportant for brittle ceramic materials as ceramics are much stronger incompression than tension. The disclosed mounting feature reducesconcentricity deflections compared to prior designs due to the fact thatthe part has a constant cross section circumferentially around themounting feature centerline The mounting feature of the presentdisclosure can be formed of a single piece, simplifying design,construction, assembly and maintenance costs. The disclosed mountingfeature will also provide for better sealing when compared with mountsutilizing drilled holes in order to achieve the required compliance. Bysupplying a complaint design, the present disclosure provides a mountingmember which will more readily maintain a larger contact area with therunner than stiffer designs.

The present disclosure further provides for a continuous support ring,spring element, radial pilot and axial flange to support a runner. Thisdisclosure provides a runner of a simpler design in order to reducecosts. The continuous support ring accommodates for differences inthermal growth between components while preventing further leakagepathways. The present disclosure advantageously protects the runner fromthe relative movement of a spring element used to generate a clampingforce.

While some of the above embodiments have been provided in the context ofa particular apparatus, it will be understood that the above embodimentsdisclose improvements to containment apparatuses used in any rotatingmachine. While preferred embodiments of the present disclosure have beendescribed, it is to be understood that the embodiments described areillustrative only and that the scope of the disclosure is to be definedsolely by the appended claims when accorded a full range of equivalence.Many variations and modifications naturally occurring to those of skillin the art from a perusal hereof.

1. A circumferential seal for a machine having a metallic rotatingshaft, said seal comprising: a metallic mounting element affixed arounda circumference of the shaft, said mounting element comprising a baseforming a radially outward facing cylindrical surface extending axiallyalong the shaft, and a mounting member extending radially outward fromthe base and axially along the shaft forming a radially inward facingcylindrical surface extending axially along the shaft a distance lessthan said radially outward facing cylindrical surface of said base; anda ceramic sealing runner having a radially outward facing cylindricalsurface extending axially along the shaft a distance greater than saidradially outward facing cylindrical surface of said base, said ceramicsealing runner being carried by said mounting element in axial andradial alignment by an interference fit between at least a portion ofsaid radially outward facing cylindrical surface of said ceramic sealingrunner and at least a portion of said radially inward facing cylindricalsurface of said mounting member.
 2. The circumferential seal of claim 1wherein said mounting member of said mounting element is radiallycompliant.
 3. The circumferential seal of claim 2, wherein said mountingmember further forms an extension projecting radially outward from thebase, an axial extending member and an axial return member which formssaid radially inward facing surface of said mounting member, whereinsaid extension, said axially extending member and said axial returnmember form a radially compliant opening in said mounting member.
 4. Thecircumferential seal of claim 3, wherein said axially extending memberis arcuate.
 5. The circumferential seal of claim 1, wherein saidmounting member further comprises a fluid flinger disposed on a radialouter surface of said mounting member.
 6. The circumferential seal ofclaim 1, wherein said sealing runner experiences its highest stress loadduring assembly.
 7. The circumferential seal of claim 1, wherein thestress load on said sealing runner decreases with increasingtemperature.
 8. The circumferential seal of claim 1, further comprisinga radial seal for sealingly engaging said outer radially outward facingsurface of said sealing runner.
 9. The circumferential seal of claim 8,wherein said radial seal comprises carbon.
 10. The circumferential sealof claim 1, wherein said interference fit is proximate an axial end ofsaid sealing runner.
 11. The circumferential seal of claim 1, whereinsaid base further forms a radially inner surface at an angle to an axisof the machine.
 12. The circumferential seal of claim 1, wherein saidradially outward facing surface of said base and said runner define anopening for operably engaging a flexible sealing element.
 13. Thecircumferential seal of claim 12, wherein said flexible sealing elementis an O-ring.
 14. A circumferential seal for a machine having a metallicrotating shaft, said seal comprising: a mounting element affixed arounda circumference of the shaft, said mounting element comprising: a baseforming a radially outward facing surface extending axially along theshaft; and a mounting member, wherein said mounting member forms anextension projecting radially outward from the base, an axial extendingmember and an axial return member which forms a radially inward facingcylindrical surface, wherein said extension, said axially extendingmember and said axial return member form a radially compliant opening insaid mounting member; and a sealing runner having a radially outwardfacing cylindrical surface extending axially along the shaft, saidsealing runner being carried by said mounting element in axial andradial alignment by an interference fit between at least a portion ofsaid radially outward facing cylindrical surface of said ceramic sealingrunner and at least a portion of said radially inward facing cylindricalsurface of said mounting member.
 15. The circumferential seal of claim14 wherein said mounting member is radially compliant.
 16. Thecircumferential seal of claim 14 wherein said sealing runner experienceshigher stresses at lower temperatures.
 17. A method of forming acircumferential seal in a machine having a metallic rotatable shaft,comprising: affixing a metallic mounting element around thecircumference of the shaft, said mounting element comprising a baseforming a radially outward facing cylindrical surface extending axiallyalong the shaft, and a mounting member extending radially outward fromthe base and axially along the shaft forming a radially inward facingcylindrical surface extending axially along the shaft a distance lessthan said radially outward facing cylindrical surface of said base; andproviding a ceramic sealing runner having a radially outward facingcylindrical surface extending axially along the shaft a distance greaterthan said radially outward facing cylindrical surface of said base, saidceramic sealing runner being carried by said mounting element in axialand radial alignment by an interference fit between at least a portionof said radially outward facing cylindrical surface of said ceramicsealing runner and at least a portion of said radially inward facingcylindrical surface of said mounting member.
 18. The method of claim 17wherein said mounting member of said mounting element is radiallycompliant.
 19. The method of claim 17 further comprising sealinglyengaging said outer radially outward facing surface of said sealingrunner with a radial seal.
 20. The method of claim 17 wherein saidsealing runner experiences its highest stress load during assembly.